Macrocyclic Copper(II) Complexes as Catalysts for Electrochemically Mediated Atom Transfer

Masnun Naher; Chuyi Su; Jeffrey R Harmer; Craig M Williams; Paul V Bernhardt

doi:10.1021/acs.inorgchem.4c00311

Macrocyclic Copper(II) Complexes as Catalysts for Electrochemically Mediated Atom Transfer

Inorg Chem. 2024 Apr 8;63(14):6453-6464. doi: 10.1021/acs.inorgchem.4c00311. Epub 2024 Mar 25.

Authors

Masnun Naher¹, Chuyi Su¹, Jeffrey R Harmer², Craig M Williams¹, Paul V Bernhardt¹

Affiliations

¹ School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia.
² Centre for Advanced Imaging, University of Queensland, Brisbane 4072, Australia.

PMID: 38526552
DOI: 10.1021/acs.inorgchem.4c00311

Abstract

Copper-catalyzed electrochemical atom transfer radical addition (eATRA) is a new method for the creation of new C-C bonds under mild conditions. In this work, we have explored the reactivity of an analogous series of N₄ macrocyclic Cu^II complexes as eATRA precatalysts, which are primed by reduction to their monovalent oxidation state. These complexes were fully characterized structurally, spectroscopically, and electrochemically. A spectrum of radical activation reactivity was found across the series [Cu^I(Me₄cyclen)(NCMe)]⁺ (Me₄cyclen = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane), [Cu^I(Me₄cyclam)(NCMe)]⁺ (Me₄cyclam = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), and [Cu^I(Me₂py₂clen)(NCMe)]⁺ (Me₂py₂clen = 3,7-dimethyl-3,7-diaza-1,5(2,6)-dipyridinacyclo-octaphane). The rate of radical production by [Cu(Me₂py₂clen)(NCMe)]⁺ was modest, but rapid radical capture to form the organocopper complex [Cu^I(Me₂py₂clen)(CH₂CN)] led to a dramatic acceleration in catalysis, greater than seen in any comparable Cu complex, but this led to rapid radical self-termination instead of radical addition.